(1) FIELD OF THE INVENTION
The present invention is concerned with a device for the thermal spray application of welding materials, comprising a jet focussing nozzle and a burner nozzle disposed therein at its feed-in end.
(2) DESCRIPTION OF THE PRIOR ART
Devices of the afore-described type for the thermal spraying of coatings of powder are disclosed in U.S. Pat. No. 4,711,627. They work with low spray losses and, operating in accordance with the so-called differential pressure principle, on the one hand, do not require more, or not much more, in terms of structural components than has so far been necessary for flame spraying and, on the other hand, through proportionate adjustability of the combustion chamber, permit the use of all combustible gases, particularly including the use of acetylene and, to a limited extent, also permit the processing of different spray powders. They also make it possible to carry out ignition or start-up procedures with safety, requiring, however, employment of a relatively complex switching sequence and a corresponding switching mechanism. For, it is imperative for the safe ignition start-up of the state-of-the-art device, and hence, for the serviceability of this device, in general, to carry out ignition in the following steps to reduce the combustible gas-oxygen mixture to a minimum for the start-up phase: scavenging with pure oxygen; making the ignition device ready for operation and only then feeding-in the combustion gas. If this order of sequence were not followed, it would lead immediately ahead of the nozzle to a dangerous explosion when the ignition is switched on, or at least to an explosion with a quenching of the flame. Admittedly, this operational sequence essential for the start-up phase could be manipulated by hand but this would be too bothersome and also too unsafe.